1. Field of the Invention
The present invention relates to power converters, and more particularly, to a control circuit providing a biased current limit used for limiting a maximum output power of power converters.
2. Background of the Invention
In recent development, many current limit schemes are proposed for limiting the output power of power converters, such as “PWM controller for controlling output power limit of a power supply” by Yang, et al, U.S. Pat. No. 6,611,439; “PWM controller having a saw-limiter for output power limit without sensing input voltage” by Yang, et al, U.S. Pat. No. 6,674,656. However, the patent '439 requires an input resistor connected to the input voltage, which causes a power loss at the input resistor. A saw-limiter of the patent '656 causes a sub-harmonic oscillation when a switching current is limited and the flux density of a transformer is high. In order to provide the solution, the present invention is directed to a method and an apparatus to limit the maximum output power of power converters without foregoing drawbacks.